Process for increasing the crystallinity and safe ironing temperature of cellulose triacetate textiles with aromatic chemical swelling agents



United States Patent 3,025,128 PROCESS FOR INCREASING THE CRYSTALLIN- ITY AND SAFE IRGNING TEMPERATURE OF CELLULOSE TRIACETATE TEXTILES WlTH AROMATIC CHEMICAL SWELLING AGENTS Donald Finlayson and Arthur Michael Goddard, Spondon, near Derby, England, assignors to British Celanese Limited, a corporation of Great Britain No Drawing. Filed Nov. 5, 1954, Ser. No. 467,223 Claims priority, application Great Britain Nov. 25, 1953 4 Claims. (Cl. 8-131) This invention relates to textile materials comprising fibres of cellulose triacetate.

in US. application Ser. No. 400,798, filed December 28, 1953, of British Celanese Limited, now US. Patent No. 2.862,785, there is described a type of cellulose triacetate textile material which is characterised inter alia by having a sticking temperature in the neighbourhood of 220240 C., as compared with the sticking temperature of about 200 C. of cellulose triacetate materials as previously made and of materials made from the more usual acetone-soluble type of cellulose acetate. (The sticking temperature is a measure of the sensitivity of the material to temperature, and for the purpose of the present specification is to be taken as the lowest temperature at which a heated iron, after standing on a fabric of the cellulose acetate for 10 seconds, causes the fabric to stick to its surface.) These new materials are obtained by subjecting cellulose triacetate materials to the action of dry heat at temperatures above about 170 C. or to the action of a heated softening agent such as steam or hot water at a temperature between about 120 and 160 C. This treatment changes the physical form of the cellulose triacetate (although not, at least to any significant extent, its chemical composition). Examination of the X-ray diagrams of the cellulose triacetate fibres before and after the treatment has confirmed that the change is accompanied by a rearrangement into a state of greater order of the macromolecules of the cellulose triacetate, or in other words an increase in the proportion of the triacetate which is in a more or less crystalline state and a decrease in the proportion which is in the socalled amorphous or substantially non-crystalline state. For the purpose of the present specification it will be convenient to refer to the new materials as materials of cellulose triacetate of an increased degree of crystallinity; similarly cellulose triacetate materials as first obtained by melt-spinning or wetor dry-spinning processes, or by completely acetylating unoriented partly acetylated cellulose filamentary materials, will be termed materials of cellulose triacetate of a normal degree of crystallinity.

Textile materials comprising fibres of cellulose triacetate of an increased degree of crystallinity have a number of advantages. One such advantage, which is of considerable commercial value, is their high safe ironing temperature. It is well known that while cellulose materials such as cotton, linen and regenerated cellulose fabrics can be ironed at temperatures up to about 240 C., at which temperature they begin to scorch, the cellulose acetate fabrics obtained in the past have been more sensitive; indeed in practice it is recommended that ironing temperatures above 170 180 C. should not be used, since unless the operator is very skilful they tend to impart a gloss or shine to the fibres. This temperature of 170-180 C. is commonly referred to as the safe ironing temperature. Other thermoplastic fibres, including nylon, have similar or lower safe ironing temperatures.

According to the invention, textile materials comprising fibres of cellulose triacetate of a normal degree of crystallinity are given a treatment in which the degree of crystallinity of the cellulose triacetate is increased by the action of an organic liquid or vapour which is a swelling agent for cellulose triacetate. An important aspect of the invention is the manufacture of textile materials made up at least in part of thermoplastic fibres and having a safe ironing temperature substantially higher than C., which comprises subjecting a textile ma terial comprising as the sole thermoplastic constituent fibres of cellulose triacetate of a normal degree of crystallinity to a treatment in which the degree of crystallinity of the cellulose triacetate is increased, and the sticking temperature of the material is raised by at least 10 C., by the action of an organic liquid or vapour which is a swelling agent for cellulose triacetate.

The term textile material is employed in this specification to denote both textile fabrics (and articles made from them) and intermediate structures used in making fabrics, such as yarns made up of continuous filaments or spun from staple fibres, and staple fibres themselves in the form of tops, slivers and other structures in which they are more or less loosely held together. The term fibres includes both continuous filaments of indefinite length and short lengths of filament such as staple fibres.

Swelling agents for cellulose triacetate differ widely among themselves as regards the temperature at which they are most effective in increasing the degree of crystallinity of the cellulose triacetate, the rate at which the degree of crystallinity increases, and the maximum increase obtainable. With some, for example the lower monohydric alcohols (i.e. alcohols containing 1-4 carbon atoms in the molecule), the increase is small, but with others the effect obtained approaches or equals that obtained by the processes of US. application Ser. No. 400,798. The swelling agents whose use is preferred are the normally liquid aromatic hydrocarbons, normally liquid alkyl halides of boiling point above 50 C., mix tures of acetone and water containing 30-70% of acetone, mixtures of acetone and a lower monohydric alcohol containing 20-70% of acetone, and vapours of very volatile solvents or strong swelling agents for cellulose triacetate, especially the vapours of methylene chloride and chloroform.

Cellulose triacetate textile materials of a normal degree of crystallinity which are to be treated in accordance with the invention may with advantage be formed by a melt spinning process, especially by a process described in US. applications Ser. Nos. 243,994, filed August 29, 1951; 292,771, filed July 10, 1952; 292,772, filed July 10, 1952, now U.S. Patent No. 2,888,711; 304,441, filed August 14, 1952; 338,834, filed February 25, 1953, now US. Patent No. 2,831,748, or 423,843, filed April 16, 1954, now U.S. Patent No. 2,742,469. In one such process, cellulose triacetate in powder form is urged (e.g. by a rapidly reciprocating tamper) against the side of a heated plate having spinning orifices therein and is fused by the heat applied to the plate, the fused ester is drawn away from the orifices in the form of filaments, and fresh powdered ester is continuously fed to the plate. The spinning orifices may be circular, or they may be in the form of slits or of two or more closely spaced or intersecting holes, as described in U.S. application Ser. No. 338,834. In another process cellulose triacetate in the form of a coherent rod or a block or tablet of uniform cros-section is pressed axially against a heated plate having spinning orifices therein. The cellulose tri acetate may contain pigments, dyes or other effect materials, as described for example in U.S. application Ser. No. 292,- 771. Wet and dry spinning methods may also be used to form the cellulose triacetate textile material. Thus solutions of cellulose triacetate in mixtures of methylene or ethylene chloride and methyl or ethyl alcohol or acetic acid, or in acetic acid alone, may be extruded as filaments and set either by means of a coagulating liquid or by an evaporative method. For example solutions of cellulose triacetate in mixtures of methylene or ethylene chloride and acetic acid may be extruded into a coagulating liquid comprising an aqueous alcohol, especially aqueous ethyl alcohol of concentration about 9095%, as described in U.S. Patent No. 2,657,973 of British Celanese Limited, or solutions in acetic acid may be extruded into aqueous acetic acid which may with advantage contain a fairly high proportion of an alkali metal or ammonium acetate, an alkaline earth metal acetate or magnesium acetate, or of some other salt.

Yet another method by which the cellulose triacetate textile meterial may be obtained is the further acetylation of a textile material comprising unorientated yarns of cellulose acetate of a lower acetyl value. For instance, yarns or fabrics of acetone-soluble cellulose acetate may be further acetylated with acetic anhydride in the presence of a diluent such as benzene, and of a basic or acid es-terification catalyst such as pyridine, sulphuric acid, or hydrochloric acid with or without a metal chloride such as zinc chloride or ferric chloride as described in British Patents Nos. 448,816, 448,817 and 448,917.

The conditions under which the treatment of the invention is carried out depend primarily on the solvent or swelling properties of the organic liquid or vapour employed. For example, aromatic hydrocarbons such as benzene, toluene and the xylenes, and alkyl halides of boiling point above 50 C. such as propyl bromide, are best used in the liquid phase and at temperatures between about 60 and 90 C. Mixtures of acetone and water containing 30-70% of acetone, and mixtures of acetone and a lower monohydric alcohol containing 20-70% of acetone, can be used at temperatures down to about C., in particular temperatures between 15 and 40 C.; the vapours of methylene chloride and chloroform are preferably employed at temperatures between 15 and 30 C. The time necessary for the production of the maximum effect also varies with the agent used. For example, benzene at its boiling point may require 3 to 7 hours, although a very useful degree of improvement is obtainable in a shorter time, e.g. 1 /2 to 2 /2 hours. Acetone-water and acetone-alcohol mixtures are particularly useful when a short time of treatment is more important than the attainment of the greatest possible increase in crystallinity, and also when it is desirable to work room temperature; thus a very useful effect can be obtained in half an hour or less, e.g. in 5-30 minutes, at temperatures in the neighbourhood of C. Methylene chloride vapour at about 20 C. may require 1 to 2 hours, and chloroform vapour somewhat longer, e.g. 3 to 4 hours, to give their maximum effect.

In the course of the treatment the textile materials tend to shrink slightly, usually by about 1% to 3%. This shrinking may be prevented by keeping the material under tension, or the material may be allowed to shrink either freely or by less than it would in the complete absence of tension.

The treatment may be applied either to individual batches of material, e.g. lengths of fabric or loosely wound yarn packages which will permit shrinking, or continuously as to a running fabric or yarn. Yarns and the like are usually best treated by a continuous method owing to the difficulty of allowing for uniform shrinkage if they are in package form. For example, they may be treated on thread-storage thread-advancing reels and like devices arranged so as to permit the desired degree of shrinkage.

Besides the high safe ironing temperature already referred to, materials of cellulose triacetate of an increased degree of crystallinity also have very good dimensional stability at high temperature. Thus they may in many cases be heated to 220 to 235 C. without undergoing much change in dimensions, whereas cellulose triacetate materials which have not been treated either in ac- 'cordance with the present invention or as described in US, application Ser. No. 400,798, and also materials made from acetone-soluble cellulose acetate, on being heated to such temperatures undergo a very considerable degree of shrinking and also suffer a serious loss of strength. Again, the tendency of cellulose triacetate textile materials to creep under load in hot water is greatly reduced by increasing the degree of crystallinity of the cellulose triacetate.

The invention is illustrated by the following examples:

Example I A fabric woven from a melt-spun cellulose triacetate yarn obtained by the process of U.S. application Ser. No. 243,994 was immersed for 6 hours in boiling benzene, after which it was well drained and finally freed from benzene by evaporation. The safe ironing temperature of the material was raised by this treatment from about 170 C. to 230 C. Another piece of the fabric was treated for only 2 hours, and its safe ironing temperature was raised to 210 C.

Example II Another piece of the same fabric was treated for 20 minutes with a mixture of equal parts by weight of acetone and Water at about 20 C., with the result that its safe ironing temperature was raised to 210 C.; when the treatment was stopped after 10 minutes the safe ironing temperature was raised to about 200 C. Treatment with a mixture of 40% by weight of acetone and 60% by weight of ethyl alcohol had a similar effect.

Example 111 Another piece of the same fabric was suspended over methylene chloride at 20 C. in a closed vessel for about 2 hours; at the end of this time the safe ironing temperature of the fabric had been raised to about 230 C.

In all these examples the effect of the treatment has been illustrated by the rise in the safe ironing temperature of the fabric, since this is a property of immediate practical importance. This rise was, of course, always accompanied by a rise in the sticking temperature and an increase in the dimensional stability of the fabric. Thus the treated fabrics could be heated to about 235 C. for 1 minute without undergoing any substantial shrinkage, whereas the untreated fabric when heated to this temperature shrank by 20 to 25%. Furthermore the tendency of the untreated fabric to creep under any specified load in water at 80 C. was reduced by up to -80%.

We have further found that in one respect the treatment of the present invention has a desirable effect which is not as a rule obtained when the cellulose triacetate textile materials of a normal degree of crystallinity are subjected to dry heat in accordance with U.S. application Ser. No. 400,798. When a cellulose triacetate material of a normal degree of crystallinity is given the dry heat treatment, its tenacity may at first be increased somewhat, but if the treatment is continued long enough to give the maximum safe ironing temperature the tenacity frequency falls back to somewhere near its original value. When cellulose triacetate material of a normal degree of crystallinity is treated in accordance with the present invention, for instance by immersion in benzene at the boiling point, its tenacity is markedly increased, the exact degree of increase depending on the previous history of the material as well as on the precise conditions under which the treatment is performed. This effect is illustrated by the following example:

Example IV A number of different multi-filament yarns of cellulose triacetate produced by melt-spinning were immersed in benzene at the boiling point for 4 hours. The resulting average increase in tenacity is shown in the following table.

Tenacity: Extensibility, percent Untreated yarns, 1.84 grams per denier 25.2 Treated yarns, 3.16 grams per denier 18.9

While the invention has been described in the examples by reference to the treatment of melt-spun cellulose triacetate materials, the treatments described therein can also be given to cellulose triacetate materials of a normal degree of crystallinity produced by other methods, especially by dry spinning methods or by the acetylation of unoriented partly acetylated cellulose materials.

Having described our invention what we desire to secure by Letters Patent is:

1. Process for the manufacture of textile materials comprising thermoplastic fibres yet having a safe ironing temperature substantially above 200 C. which comprises bringing a textile material comprising as the sole thermoplastic constituent fibres of cellulose triacetate which is in that crystalline state in which fibres thereof have a sticking temperature of about 200 C. into contact with an aromatic hydrocarbon chemical swelling agent for cellulose triacetate which is non-reactive therewith and which is liquid at atmospheric pressure and ordinary temperatures, the said hydrocarbon being in the liquid phase and at a temperature of 60-90 C. for a period of time which is at least 1 hours in length and is also at least sufficient to raise the sticking temperature by 10 C.

2. Process according to claim 1, wherein the textile material is maintained in contact with the hydrocarbon at the said temperature of 6090 C. for 3 to 7 hours.

3. Process according to claim 1, wherein the textile material consists entirely of the cellulose triacetate fibres.

4. Process according to claim 2, wherein the textile material consists entirely of the cellulose triacetate fibres.

References Cited in the file of this. patent UNITED STATES PATENTS 1,935,263 Ellis Nov. 14, 1933 2,070,583 Dickie Feb. 16, 1937 2,198,660 Dreyfus Apr. 30, 1940 2,328,682 Schnegg Sept. 7, 1943 2,347,001 Schnegg Apr. 18, 1944 2,862,785 Finlayson et al Dec. 2, 1958 FOREIGN PATENTS 438,786 Great Britain Nov. 21, 1935 450,936 Great Britain July 23, 1936 534,775 Great Britain Mar. 18, 1941 570,588 Great Britain July 13, 1945 OTHER REFERENCES 25 801 and 804.

Baker: Journal of the American Chemical Society, vol. 64, April 1942, pages 776-782. 

1. PROCESS FOR THE MANUFACTURE OF TEXTILE MATERIALS COMPRISING THERMOPLASTIC FIBRES YET HAVING A SAFE IRONING TEMPERATURE SUBSTANTIALLY ABOVE 200* C. WHICH COMPRISES BRINGING A TEXTILE MATERIAL COMPRISING AS THE SOLE THERMOPLASTIC CONTITUENT FIBRES OF CELLULOSE TRIACETATE WHICH IS IN THAT CRYSTALLINE STATE IN WHICH FIBRES THEREOF HAVE A STICKING TEMPERATURE OF ABOUT 200* C. INTO CONTACT WITH AN AROMATIC HYDROCARBON CHEMICAL SWELLING AGENT FOR CELLULOSE TRIACETATE WHICH IS NON-REACTIVE THEREWITH AND WHICH IS LIQUID AT ATMOSHERIC PRESSURE AND ORDINARY TEMPERATURE, THE SAID HYDROCARBON BEING IN THE LIQUID PHASE AND AT A TEMPERATURE OF 60*-90* C. FOR A PERIOD OF TIME WHICH IS AT LEAST 11/2 HOURS IN LENGTH AND IS ALSO AT LEAST SUFFICIENT TO RAISE THE STICKING TEMPERATURE BY 10* C. 